Certain electronic chips, such as bank card chips, may contain confidential data which may be coveted by pirates. Such confidential data may be contained in circuits located on the front surface side of the chip. To obtain the data, a pirate may carry out an attack from the back side of the chip.
In a type of attack, called etch attack, the pirate etches a portion of the back side of the chip. From this etched portion, the pirate makes cavities having a width of a few micrometers, for example, by using an ion beam, which extend towards the front side until the circuits have been reached. Electric contacts with circuit elements are then created in the cavities, and the pirate uses these contacts to analyze the chip in operation.
In another type of attack, the pirate for example scans the back side of the chip with laser pulses. The impact of the laser disturbs the chip operation. The observation of the consequences of such disturbances on the activity of the circuits enables the pirate to successfully complete the attack. To disturb the chip operation, the pirate may also apply positive or negative potentials by means of a probe in contact with the back side, or induce currents or voltages in elements of the circuits by means of a coil arranged close to the back side. This type of attack is called fault injection attack.
Such a chip comprising confidential data may be comprised in a stack of interconnected chips.